Apparatus for fluid control with a substrate processing tank

ABSTRACT

An improved method and apparatus for adjusting chemistry concentrations and temperatures within a substrate processing tank is provided. A first aspect may include checking the fluid level within the tank, and, if the level is higher than a predetermined upper level, bleeding an amount of fluid from the tank; if the level is lower than a predetermined lower level, flowing an amount of fluid to the tank, and if the level is between the predetermined upper and lower levels, bleeding an amount of fluid from the tank and flowing an amount of fluid to the tank. A second aspect may include flowing water into the tank at a flow rate at least equivalent to the flow rate of water required to achieve a chemistry spike of a predetermined concentration and volume prior to beginning the flow of chemicals. A third aspect may include a method and apparatus for heating or cooling chemistry to a predetermined temperature as the chemistry is recirculated.

[0001] This application is a division of U.S. patent application Ser.No. 09/580,881, filed May 30, 2000, which claims priority from U.S.provisional application Serial No. 60/136,911, filed Jun. 1, 1999, bothof which are hereby incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

[0002] The present invention relates to a method and apparatus forpromoting uniform processing within a substrate processing tank. Morespecifically, the present invention relates to a method and apparatusfor controlling fluid temperatures and chemical concentrations within atank used for semiconductor processing, such as a megasonic tank.

BACKGROUND OF THE INVENTION

[0003] In the field of semiconductor processing, it is important toensure that each processed wafer (e.g., patterned, or unpatterned, etc.)experiences identical processing conditions so as to ensure consistentquality. Bath-type processes present particular process uniformityissues. Evaporation, chemistry decomposition and process temperatureeach vary over time. For example, conventional megasonic tank-typecleaners submerge a wafer in a tank of cleaning chemistry, typicallycomprising a mixture of deionized water, ammonia and hydrogen peroxide.To achieve desired cleaning performance, the concentration of eachcomponent is carefully controlled as the tank is filled with chemistry.However, as ammonia quickly evaporates, and hydrogen peroxide readilydecomposes (forming water and oxygen) the concentration of eachcomponent immediately begins to change.

[0004] Further, the chemistry is heated to a desired temperature as thechemistry flows into the tank. To achieve desired cleaning performanceand ensure consistent quality wafers, the chemistry is maintained withina close tolerance of the desired temperature. However, duringprocessing, the heat generated by the transducers which megasonicallyenergize the chemistry also undesirably heat the chemistry. Thisundesirable heating of the chemistry not only causes processingvariations, but also further accelerates the rate of chemicalevaporation and decomposition.

[0005] To combat the process drift described above, test wafers areperiodically processed in a megasonic tank, and the chemicalconcentration of the bath is adjusted based on the cleanliness of thetest wafers. This method is labor intensive and subject to human error.Moreover, system productivity is decreased by the need to run testwafers. Alternative methods continuously bleed chemistry from the tankwhile feeding fresh chemistry to the tank. These methods require hugeenergy consumption to heat the continuous volume of chemistry flowing tothe tank.

[0006] Accordingly, a need exists for an improved method and apparatusfor controlling temperature and concentration of chemistries within asubstrate processing tank such as a megasonic tank.

SUMMARY OF THE INVENTION

[0007] The present invention provides an improved method and apparatusfor adjusting chemistry concentrations and temperatures within asubstrate processing tank. In a first aspect the inventive methodcomprises checking the fluid level within the tank, and, if the level ishigher than a predetermined upper level, bleeding an amount of fluidfrom the tank; if the level is lower than a predetermined lower level,flowing an amount of fluid to the tank, and if the level is between thepredetermined upper and lower levels, bleeding an amount of fluid fromthe tank and flowing an amount of fluid to the tank.

[0008] In a second aspect, the inventive method comprises flowing waterinto the tank at a flow rate at least equivalent to the flow rate ofwater required to achieve a chemistry spike of a predeterminedconcentration and volume (e.g., 50 ml/minute water for a 210 ml/minuteflow rate of 5 parts water and 2 parts chemical), prior to beginning theflow of chemicals.

[0009] In a third aspect, the invention provides a method and apparatusfor heating or cooling chemistry to a predetermined temperature as thechemistry is recirculated.

[0010] Each aspect of the invention may be automated, in the form of aprogram product, and therefore may reduce the labor costs associatedwith many conventional methods. Each aspect also may exhibit its ownadvantages, for instance the first aspect of the invention may conserveboth energy and chemistry, as chemistry is only periodically flowed intothe tank, requiring less chemistry and less energy to heat and pump thechemistry. The second aspect may prevent harmful concentrations ofchemistry from being released, and the third aspect may reduceevaporation and decomposition rates. Each aspect of the invention mayreduce process drift, increase processing uniformity and the uniformquality of wafers processed thereby.

[0011] Other features and advantages of the present invention willbecome more fully apparent from the following detailed description ofthe preferred embodiments, the appended claims and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a schematic side elevational view of the inventiveapparatus for fluid control within a substrate processing tank;

[0013]FIG. 2 is a flow chart useful for describing a first aspect of theinvention; and

[0014]FIG. 3 is a flow chart useful for describing a second aspect ofthe invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a schematic side elevational view of an inventive fluidflow system 10 for controlling fluid within a tank-type substrateprocessing system, such as an exemplary megasonic tank 11 having atransducer 13 coupled thereto so as to transmit sonic energy to fluidcontained within the tank 11. Also coupled to the tank 11 are anoverflow weir 15 having a high fluid level detector 17 and a low fluidlevel detector 19, a fluid inlet 21 (coupled to the tank 11) and a fluidoutlet 23 (coupled to the overflow weir 15). Coupled between the fluidinlet 21 and the fluid outlet 23 is a fluid recirculation loop 25. Thefluid recirculation loop 25 comprises a pump 27, a temperaturecontroller 29 and a filter 31, such that fluid is pumped from the fluidoutlet 23 through the pump 27, the temperature controller 29 and thefilter 31 prior to returning to the tank 11 via the fluid inlet 21.Coupled to the fluid recirculation loop 25 is a fluidlevel/concentration system 33 comprising a liquid delivery module 35comprising, for example, a source of deionized water 37, a source ofammonia 39 and a source of hydrogen peroxide 41. Each of the fluidsources 37, 39 and 41 is coupled to a mixing chamber 43 via a valve 45,47 and 49, respectively. An outlet line 51 of the mixing chamber 43couples a valve 53 prior to coupling to the fluid recirculation loop 25between the fluid outlet 23 of the overflow weir 15 and the pump 27. Thefluid flow system 10 also comprises a drain line 50 which is coupled tothe fluid recirculation loop 25 between the temperature controller 29and the filter 31. The drain line 50 is coupled to a drain 57 via arestrictor 59.

[0016] A controller 61 operatively couples to the transducer 13, thepump 27 and the temperature controller 29. Also, the controller 61couples to the high fluid level detector 17, the low fluid leveldetector 19, the valves 45, 47 and 49, and the valve 53. A program whichmay be stored within the controller 61, or may be read by the controller61 from a carrier such as a floppy disc, or an electronic signal from aremote location (e.g., a computer networked to the controller 61 locallyor via an intra or internet, etc.) controls the operation of theinventive fluid flow system 10. The program which controls performanceof the inventive method is described further with reference to FIGS.2-3.

[0017] In operation, assuming an exemplary chemistry recirculation rateof 210 ml/minute and assuming a safe maximum chemical concentrationspike of five parts deionized water, one part ammonia and one parthydrogen peroxide (i.e., a 5-1-1 concentration), the valve 45 ismanually set for a minimum flow rate of at least 150 ml/minute, and thevalves 47 and 49 are each manually set for a maximum flow rate of 30ml/minute, and the valve 53 is set for a maximum flow rate of 210ml/minute. For example, the valves 45, 47 and 49 may be provided withfactory preset flow switches which set a minimum flow rate (e.g., a flowswitch 45 a which sets a minimum flow rate of 150 ml/min for deionizedwater flow control valve 45) or a maximum flow rate (e.g., a flow switch47 a and a flow switch 49 a which set a maximum flow rate of 30 mL/minfor ammonia and hydrogen peroxide flow control valves 47, 49,respectively). The flow switches may be hard-interlocked to the chemicalvalves 45, 47 and 49. Tripping any of the flow switches will shut downthe liquid delivery module 35. Additionally there may be manual flowcontrollers 45 b-49 b (e.g., manual flow meters) which manually controlthe flow rates to the valves 45-49, respectively. For example, the flowcontrollers 45 b-49 b may be manually set to allow any mixing ratio ofthe deionized water, ammonia and hydrogen peroxide within safety limits(e.g., 200 mL/min for deionized water valve 45 b, 20 mL/min for ammoniavalve 47 b and 20 mL/min for hydrogen peroxide 49 b). Thereafter, thetank 11 is filled with a desired chemical concentration, for example,six parts deionized water, one part ammonia, and one part hydrogenperoxide (i.e., a 6-1-1 concentration). In this example the spike is setto be of higher concentration than the chemistry contained in the tank,so as to compensate for decomposition. However, if decomposition doesnot occur and only fluid level varies, the spike would be set to thesame concentration as the fluid within the tank 11.

[0018] As particles are cleaned from a wafer, they tend to collect onthe surface of the chemistry bath. To prevent such particles fromre-adhering to a wafer as the wafer is lifted from the bath, fluid iscontinuously flowed into the tank 11 via the fluid inlet 21 at aconstant rate (e.g., 10 ml/minute), causing the fluid and the particlesfloating thereon to overflow into the overflow weir 15. Accordingly, ifno processing variables existed, the fluid level in the overflow weir 15would maintain a constant level. However, due to evaporation and due tothe fact that a certain amount of fluid adheres to the surface of eachwafer as the wafer is removed from the tank, the fluid level in theoverflow weir 15 varies. Detection of a low level indicates that fluidand particles are not being sufficiently flushed into the overflow weir15, and, depending on the particular chemistry may indicate rapidevaporation. Detection of a high level indicates that evaporation andprobably decomposition (which often occurs when evaporation occurs) ifthe chemistry is known to decompose, is occurring. Accordingly, tocombat the problems of insufficient flush rate and chemistryconcentration variation, the controller 61 is programmed to periodicallycheck the high fluid level detector 17 and the low fluid level detector19 to determine whether the fluid level in the overflow weir 15 isabove, below or within the desired range (e.g., between the high fluidlevel detector 17 and the low fluid level detector 19 and to spikeand/or drain chemistry to and from the tank 11 to correct concentrationvariations and flush rates, as best understood with reference to FIG. 2.

[0019] The description of FIGS. 2-3 will assume the exemplary processconditions described below. Assume that the tank 11 has been filled witha 6-1-1 concentration of deionized water, ammonia and hydrogen peroxide,respectively, which is heated to 65° C. as it flows through thetemperature controller 29. Because ammonia and hydrogen peroxide areknown to readily evaporate and decompose, respectively, in this examplea 30 sec, 100 cc/minute chemistry spike of 5-1-1 concentration ofdeionized water, ammonia and hydrogen peroxide, respectively, isperiodically desired. The volume and concentration of the spike, and thedesired frequency of the spike is determined based on test results forthe specific process (e.g., chemistry, temperature, tank configuration,acoustic energy levels, process time, wafer size, etc.), as will bereadily determinable by workers of ordinary skill in the art. Toadequately flush particles from the overflow weir 15, the pump 27continuously pumps fluid from the overflow weir 15, through thetemperature controller 29 and the filter 31 and back into the tank 11via the fluid inlet 21 at a rate of 10 l/minute. The various aspects ofthe invention will be described with reference to FIGS. 2-3 withreference to the exemplary process conditions provided above.

[0020]FIG. 2 is a flow diagram useful for describing a first aspect ofthe inventive fluid control system. In block 211 the controller 61checks to see whether a predetermined period has elapsed (e.g., whethera predetermined period of time has elapsed and/or a predetermined numberof wafers have been cleaned). If the predetermined period has elapsed,the controller checks the fluid level within the overflow weir 15 (block213), and determines whether the level is high, low or normal based onreadings from the high fluid level detector 17 and the low fluid leveldetector 19 (block 215).

[0021] Thereafter, if the fluid level in the overflow weir 15 is high,the controller 61 causes the valve 59 to open to an extent, and for aperiod of time sufficient to bleed a predetermined amount of fluid fromthe tank 11 (block 217). Preferably the amount of fluid bled from thetank 11 is equal to the amount of fluid supplied to the tank 11 during aspike, in this example 100 cc/minute for 30 seconds. If the fluid levelin the overflow weir 15 is low, the controller 61 causes the valve 53 toopen to an extent, and for a period of time sufficient to spike apredetermined amount of chemistry (in this example 100 cc/minute for 30seconds) to the tank 11 (block 219). If the fluid level in the overflowweir 15 is normal (e.g., between the high fluid level detector 17 andthe low fluid level detector 19) the controller 61 causes the restrictor59 to open so as to bleed a predetermined amount of fluid (in thisexample 100 cc/minute for 30 seconds) from the tank 11, whilesimultaneously causing the valve 53 to open so as to spike apredetermined amount of chemistry (in this example 100 cc/minute for 30seconds) to the tank 11 (block 221). After the predetermined amount offluid is flowed to and/or bled from the tank 11 (blocks 217, 219 and221), the controller program proceeds to block 223 which returns toblock 211 to again determine or monitor whether a predetermined periodhas elapsed. The specific method for safely flowing the predeterminedamount of chemistry to the tank 11 is described in detail with referenceto FIG. 3.

[0022]FIG. 3 is a flow diagram useful for describing a second aspect ofthe invention which ensures safe chemistry concentrations are spiked tothe tank 11. Accordingly, FIG. 3 describes a plurality of program stepsthat are preferably performed as part of blocks 219 and 221 of FIG. 2.

[0023] After the controller 61 determines that a spike is needed (asdescribed with reference to block 215 of FIG. 2) the controller 61causes the source of deionized water 37 to open to an extent sufficientto allow a flow rate equivalent to the flow rate of deionized waterrequired to achieve a predetermined concentration and volume ofchemistry to be flowed to the liquid delivery module 35 (block 311). Inthis example for a desired 100 cc/minute flow rate of a 5-1-1concentration the source of deionized water 37 opens so as to flow 50cc/minute of deionized water. Thereafter, the controller 61 monitors theflow rate of deionized water through the source of deionized water 37 todetermine when the flow rate reaches 50 cc/minute (block 313). As soonas a 50 cc/minute flow rate of deionized water is flowing through thesource of deionized water 37 the controller 61 opens the source ofammonia 39 and the source of hydrogen peroxide 41 to an extent such that10 cc/minute can flow through each valve 47, 49 (block 315). In thismanner, by ensuring that the desired flow rate of deionized water isreached prior to flowing any chemistry, the inventive fluid controlsystem is programmed to ensure that the concentration level of chemistrydoes not exceed the 5-1-1 desired concentration. Therefore, thesubstrate is not subjected to pockets of higher concentration chemistrywhich may cause non-uniform cleaning, or may etch or degrade thesubstrate's surface. Further, because the valves 47 and 49 which controlthe flow rate of ammonia and hydrogen peroxide, respectively, aremanually set to 10 cc/minute (as previously desired) the hardware actsas a fail safe preventing more than 1 part of each chemistry fromflowing to the tank 11. Accordingly, large quantities of chemistry areprevented from flowing, and the possibility of flammability, high levelsof fumes, etc., is reduced.

[0024] The controller 61 continues to monitor the flow rate of at leastthe deionized water (block 317). If the deionized water flow rate dropsbelow the predetermined rate (e.g., 50 cc/minute) (block 319) thecontroller 61 stops the chemistry flow (block 321) and may restart thechemistry flow program (block 322) (or may be programmed to restart onlyif less than a preset amount of fluid has flowed to the tank, etc.).Otherwise, if the deionized water flow rate is not below thepredetermined 50 cc/minute, the controller 61 will continue the flow ofchemistry to the tank 11 until the desired volume (e.g., 50 cc) has beenadded to the tank (block 323). After the desired volume (e.g., 50 cc)has been added to the tank 11, the controller 61 closes the valves 45,47, 49 and 53, stopping the flow of chemistry to the tank 11 (block325).

[0025] As the chemistry flows from the liquid delivery module 35 to thetank 11 it passes through the temperature controller 29 and is heated toa predetermined temperature (e.g., 65° C.). Preferably the temperatureof the chemistry which is bled from the tank (as described withreference to blocks 217 and 221) also flows through temperaturecontroller 29 and therefore aids in preheating the chemistry spike, andin making the concentration of the spike more uniform with the existingchemistry within the tank 11.

[0026] Further, the temperature controller 29 heats or cools the fluidflowing therethrough to a predetermined temperature or range oftemperatures. Thus, if the transducer 13 has heated the tank fluidbeyond the preset temperature or range of temperatures, the temperaturecontroller 29 cools the recirculating fluid, reducing the rate ofevaporation. By mixing the incoming chemistry spike with therecirculating fluid the recirculating fluid is cooled and the chemistryspike is heated, reducing the energy required by the temperaturecontroller 29 to maintain the fluid flowing therethrough at thepredetermined temperature.

[0027] The foregoing description discloses only the preferredembodiments of the invention, modifications of the above disclosedapparatus and method which fall within the scope of the invention willbe readily apparent to those of ordinary skill in the art. For instance,although each aspect of the invention is preferably employed within aprocessing tank's fluid control system, each aspect of the invention canbe used alone or in combination with any of the remaining aspects. Forexample, in simpler form, the invention may comprise an apparatus forselectively heating and cooling the recirculating fluid, with or withoutmixing recirculating fluid with incoming chemistry spikes; may comprisespiking and/or bleeding chemistry to and from the tank based on high andlow level readings of fluid contained in the tank itself or in the weir,with or without the steps of ensuring desired deionized water flow priorto beginning chemistry flow, and with or without the hardware fail safedesign.

[0028] Accordingly, while the present invention has been disclosed inconnection with the preferred embodiments thereof, it should beunderstood that other embodiments may fall within the spirit and scopeof the invention, as defined by the following claims.

The invention claimed is:
 1. An apparatus for controlling fluid flow toa semiconductor processing tank, the apparatus comprising: a tank; afluid recirculation loop adapted to bleed fluid from the tank, to filterthe fluid and to return the fluid to the tank; and a thermo couplecoupled to the fluid recirculation loop so as to heat or cool the fluidto a predetermined temperature.
 2. The apparatus of claim 1 wherein thetank comprises a substrate support adapted to support a semiconductorsubstrate; and a transducer adapted to direct acoustic energy throughfluid contained in the tank, to the surface of a semiconductor substratesupported by the substrate support.